Effects of different rootstock and scion seedling ages on the healing and physiological traits of cucumber grafted seedlings by oblique cutting method

【Objective】 To study the effect of rootstock and scion seedling age on the healing and physiological traits of cucumber grafted seedlings，explore the suitable rootstock and scion seedling age for Hainan cucumber grafted seedling production，which could provide scientific basis for the application and promotion of Hainan cucumber grafted seedling technology. 【Method】 Using Chiyu 505 as the cucumber scion variety and Chuangfan No.1 as the rootstock，the oblique insertion method was used for grafting. Three groups of scion seedling ages（the cotyledon was slightly spread，the cotyle‐ don was flat，and the first true leaf was exposed）and two groups of rootstock seedling ages（the first true leaf was exposed and the first true leaf was flat）were set up for a total of six treatments. The effects of different rootstock and scion seedling ages treatments on the survival rate，average daily dry weight growth（G value），root-shoot ratio，strong seedling index，root vitality，chlorophyll content，antioxidant enzyme activity and anatomical structure of grafting healing process were studied using the commonly used grafting cotyledon micro expansion and the first true leaf of rootstock treatments as controls（CK）in Hainan factory seedling cultivation. 【Result】 The survival rate of cucumber grafted seedlings treated with micro expansion of scion cotyledons and flat expansion of the first true leaf of rootstock was the highest，reaching 92.0%. The G values of the three grafting treatments with rootstock seedling age of the first true leaf spreading were significantly higher than those of other treatments（P<0.05，the same below）. The root-shoot ratio of the two grafting treat‐ ments with scion seedling age of cotyledon spreading was significantly higher than that of other treatments. The strong seedling index of the grafting treatment with scion seedling age of cotyledon spreading and rootstock seedling age of the first true leaf spreading was the highest，at 0.012. The root activity and chlorophyll content were highest in the treat‐ ments of scion cotyledon micro expansion and rootstock first true leaf flat expansion，with values of 381.09 μg/ （g·h） and 35.15 mg/g respectively. The root activity was significantly higher than other combinations，and the chlorophyll content was significantly higher than that in the treatments of scion first true leaf open heart and rootstock first true leaf flat expansion. Within 10 d after grafting，the activity of peroxidase（POD）showed an overall upward trend，the activity of polyphenol oxidase（PPO）in all treatments showed an initial increase followed by a decrease，and the activity of phenylalanine ammonia lyase（PAL）showed an initial decrease followed by a rapid increase. All three antioxidant enzyme activi‐ ties performed well in the micro expansion of scion leaves and the flat expansion of the first true leaf of rootstock，significantly higher than CK and other treatments. Observing the anatomical structure of grafted seedlings，it was found that the healing condition was better when the scion was slightly expanded from cotyledons and the first true leaf of the rootstock was flattened. 【Conclusion】 There are great differences in the survival rate and quality of cucumber grafted seedlings with different rootstock-scion seedling age combinations. Based on comprehensive analysis，the appropriate rootstock seedling age for cucumber grafted seedlings using oblique insertion method in winter and spring seasons in Hainan is when the scion cotyledons being slightly expanded and the first true leaf of the rootstock being flat.